The objective of this work is to develop the chemistry required for the construction of several conformationally restricted thyroliberin (TRH) and substance P analogs. The analogs are to be used to "map" the three dimensional requirements of TRH binding to its endocrine receptor site and substance P to its NK1 receptor. After completion of biological testing, and molecular modeling, synthesis will be used interactively in order to design second and third generation analogs in the hope of optimizing biological activity.